1. Field of the Invention
This invention relates to improvements in low-noise-level internal combustion engines.
2. Description of the Prior Art
It is common knowledge that a very considerable degree of noise abatement can be achieved in internal combustion engines by the provision of outer casings which are secured in a resonance or sound-absorbing manner relative to the engine assembly housed therewithin.
One way in which this can be done is by fitting an existing engine assembly with an outer housing or casing which is not wetted by the oil. However, even the most carefully designed casings of this kind will always add to the weight and volume of the construction, and for this reason their practical application is primarily confined to existing engines of conventional or standard construction.
However, in designing new engines it is advisable to make appropriate provisions from the start for the above-mentioned principle of construction. In an existing arrangement of this kind the conventional closed-side-wall crankcase has been converted into a skeletal type of engine-unit support without side walls in the region of the main bearings, with the major resulting advantage of overall weight reduction. An outer casing which encloses the engine is mounted in an acoustically insulated manner with the aid of individual rubber elements, and the casing comprises two main parts. A lower part has the function of sealing the oil- or sump-area relative to the exterior, whilst the upper part is dry and encases the cylinder head as well as the auxiliary means and devices for the engine, all of which are accommodated in this upper dry area.
In this existing arrangement the lower, oil-wetted part is separated from the dry upper area by means of a resilient seal which encloses the skeletal type engine-unit-support in frame-like manner, and by a rear oil-sump wall with sound-absorbing annular elements inserted therein in the region of the connection for the skeletal engine-unit support and the flywheel casing. The dry enclosed flywheel casing is connected by a flange in conventional manner to a multi-speed gear box which latter, being also subject to resonant vibration from the engine, must of course also be enclosed, or it may be mounted separately from the engine and be driven through a transmission shaft, which naturally increases overall length.
It is the aim of this invention to provide an improvement in internal combustion engines of the kind in which resonance vibrations of the engine parts are not transmitted to the crankcase and the other members connected thereto.